1. Field of the Invention
This invention relates to a flat type image display apparatus comprising an electron source.
2. Related Background Art
In recent years, lightweight and slim so-called flat type image display apparatuses are drawing attention and expected to rapidly replace conventional heavy and plumpy display apparatuses that comprise a cathode ray tube. While tremendous research efforts have been paid in the technological development of liquid crystal displays in order to realize a slim and flat profile, they are accompanied by the problem of a rather dark view screen and a limited viewing angle along with other problems. An emission type flat type display apparatus comprising an electron source for emitting electron beams and a phosphor that produces visible images when irradiated with electron beams is advantageous in that it has a bright screen and a wide viewing angle and therefore can adapt itself to a large screen arrangement and highly defined images if compared with a liquid crystal display. The demand for emission type flat panel display apparatuses is remarkably increasing because of these and other advantages.
An emission type flat type image display apparatus that utilizes electron beams for producing images typically comprises a number of electron-emitting devices arranged in the form of a matrix between a face plate and a rear plate. A number of flat type image display apparatuses comprising surface conduction electron-emitting devices for emitting electron beams and a phosphor for displaying images when irradiated by accelerated electron beams have already been disclosed and applied for patent, including those invented by the applicant of the present patent application. (See inter alia Japanese Patent Publication No. 3-261024.)
FIG. 10 of the accompanying drawings is a simplified schematic sectional view of a typical flat type image display apparatus comprising surface conduction electron-emitting devices as mentioned above.
Referring to FIG. 10, the image display apparatus comprises a substrate 1001 made of an insulating material such as soda lime glass, a number of surface conduction electron-emitting devices 1002 arranged on the substrate 1001, an insulation layer 1003 formed on the substrate 1001 and grids 1004, each having a hole for allowing electron beams to pass therethrough and operating as a modulation electrode. The apparatus further comprises a face plate 1005 made of soda lime glass and provided on the inside with a phosphor 1006 covered by a metal back 1007 of aluminum thin film and a lateral frame 1009 disposed between and bonded to said substrate 1001 and said face plate 1005 by means of frit glass 1008 to form a sealed envelope. The surface conduction electron-emitting devices 1002 and the grids 1003 are electrically connected to an external drive circuit (not shown), while the metal back 1007 is electrically connected to a high voltage power source 1013 by way of a high voltage power cable 1014.
FIG. 11 is a perspective view of a surface conduction electron-emitting device 1002, showing its configuration in detail.
Referring to FIG. 11, it comprises a pair of device electrodes 1102 and 1103 separated from each other by a predetermined distance L and a thin film 1104 prepared by applying an organic palladium compound (e.g., ccp-4230: available from Okuno Pharmaceutical Co., Ltd.) onto the device and having an electron-emitting region 1105 produced in the thin film by subjecting the latter to an electrically energizing process called "forming". "Forming" is a process in which a voltage is applied between the device electrodes 1102 and 1103 to partly destruct, deform or modify the composition of the thin film 1104 and to produce an electron-emitting region 1105 which is electrically highly resistant.
The electron-emitting region 1105 may be an area of the thin film 1104 having fissures. If such is the case, electrons are emitted from and near the fissures. Proposed materials that can suitably be used for the thin film of a surface conduction electron-emitting device include SnO.sub.2, Au G. Dittmer: "Thin Solid Films", 9, 317 (1972)!, In.sub.2 O.sub.3 /SnO.sub.2 M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)! and carbon H. Araki et al.: "Vacuum", Vol. 26, No. 1, p. 22 (1983)!.
When the internal pressure of the above described image display apparatus is held to about 10.sup.-6 Torr and a drive pulse voltage is applied to the device electrodes 1102 and 1103 of the surface conduction electron-emitting device having a configuration as shown in FIG. 11 by the external drive circuit, the device emits an electron beam. The electron beam then passes through the corresponding grid 1004 and is accelerated by the positive voltage being applied to the phosphor 1006 and the metal back 1007 by the high voltage power source 1013 to eventually collide with the phosphor 1006 and make it emit light. The speed at which the electron beam travels can be controlled by the voltage applied to the grid 1006 by the drive circuit (not shown) so that consequently the fluorescent body may emit light in a controlled manner to produce an intended image on the screen.
Electron-emitting devices other than those of the surface conduction type include those utilizing thermoelectron sources, field emission electron-emitting devices W. P. Dyke & W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 5248 (1976)! and metal/insulation layer/metal electron-emitting devices C. A. Mead, "The tunnel-emission amplifier", J. Appl. Phys., 32, 646 (1961)!.
In any of the above mentioned image display apparatuses, heat is inevitably generated therein when electrons are made to collide with a phosphor for emission of light, when electron-emitting devices are electrically energized to emit electrons and/or when electron-emitting devices arranged on a plane are sequentially driven to operate by way of wires.
As heat is generated, the substrate 1001 and the face plate 1005 of the apparatus are heated to show a temperature difference between them and/or an uneven thermal distribution within the apparatus, which can in turn result in a differentiated thermal expansion that may give rise to a distorted display screen, a color breakup and/or other problems. These problems will be serious when the image display apparatus has a large display screen.